| What happens as a result of a positive/negative tropism? | positive tropisms – the plant grows towards the stimulus
negative tropisms – the plant grows away from the stimulus |
| What's Geotropism (P&N) & What happens when a plant is placed horizontally? | A response to the stimulus of gravity.
- Stem growing against force of gravity - negative geotropism
- Root growing in the direction of the force of gravity - positive geotropism
In a plant placed horizontally: bottom of the root contains more auxin ∴ grows less ∴ the root grows in the direction of gravity, bottom of stem contains more auxin ∴ grows more ∴ stem grows upwards against gravity |
| PRACTICAL: Investigate effect of light/gravity on the growth of newly germinated seedlings (7 Stages) | - Germination: beginning of plant growth, plant will continue to grow if correct conditions are available
- Mustard or cress seeds are a good choice as they grow fast & their roots & stems are clearly visible
METHOD:
1) Put cotton wool into three petri dishes, add same volume of water to each dish
2) Add ten seeds to each dish, place them in a warm place where they won’t be disturbed
3) Allow the seeds to germinate, and add more water if the cotton wool dries out
4) Once the seeds have germinated, ensure the petri dishes each contain the same number of seeds, remove any extra seeds if necessary
5) One petri dish will sit in full light on a windowsill, the second in a dark cupboard, the final dish in partial light
6) Every day for one week, measure the height of each individual seedling and record the results in a table
7) Calculate mean of the seedlings each day, and compare the mean heights in the three different locations |
| Phototropism in the Root VS Stem | PHOTOTROPISM:
- Plant stem: responses to light - positive phototropism, stem grows towards light
- Plant root: responses to light - negative phototropism, root grows away from light |
| What are auxins and what do they do? | AUXINS(a family of plant hormones):
- mostly made in the tips of the growing stems and roots, which are known as apical meristems, and can diffuse to other parts of the stems or roots
- control the growth of plants by promoting cell division and causing elongation in plant cells
- High concentration of auxins: in stems = grow more; in roots = grow less (in roots, shaded side contains more auxin ∴ grows towards light. in stems, shaded side contains more auxin ∴ bends away from light) |
| What are Gibberellins? | GIBBERELLINS:
- Group of plant hormones responsible for growth & development, important for initiating seed germination. Low concentrations can be used to increase the speed of germination - they stimulate cell elongation and cause plants to grow taller (naturally produced by seeds)
- end seed dormancy (seed dormancy must be broken down for seeds to germinate)
- promote flowering
- increase fruit size |
| How is ethene used to slow the ripening of Bananas? | ETHENE:
- A hydrocarbon which speeds the ripening of bananas & controls cell division during plant growth
- Foods often picked unripe, transported (prevents over-ripening during journey)
- Ethene is added during storage then taken to shops
- Its effect is visible, if you keep them in a bowl with other fruit, it causes them to ripen v/quickly |
| The Use of Hormones in Weedkillers | WEEDKILLERS:
- Selective weed killers(kill specific plants). contains a growth hormone that causes the weeds to grow too quickly and die. most weeds have broader leaves than grass or wheat, the weed killer is absorbed in larger quantities
- Selective weed killers kill plants that some species of animals rely on as a food source. This can result in a reduction of biodiversity
- Eg, removing dandelions in a lawn without killing grass |
| The Use of Hormones in Rooting Powder | ROOTING POWDER:
- Plant cuttings can be dipped in hormone rooting powder before planting
- Synthetic plant hormones are used to control plant growth
- Eg, rooting powder contains growth hormones that make stem cuttings develop roots quickly |
| The Use of Hormones in Promoting Growth in Tissue Culture | PROMOTING GROWTH IN TISSUE CULTURE:
- a technique used to grow whole new plants from small sections of a parent plant
- Hormones are used to stimulate cell division and elongation |
